more of a sandbox than an idle game.
Idle:
Focusing on automation and minimal player interaction, idle games let you watch progress unfold over time. Players often engage in occasional interactions like upgrades to influence growth rates or efficiencies, while the game typically accumulates resources autonomously.
Sandbox:
A game in which the player is not constrained to achieving specific goals and has a large degree of freedom to explore, interact with, or modify the game environment
Well I have to admit that you are right, I have put the idle tag on it, because it felt a semi-idle experience for me. However I did not made my homework and research what an idle game actually is, and what people expect from them (like incremental growth in the background).
GopherSand is literally a sandbox game; you are the invisible almighty gopher who can put elements in this empty box and watch them interact, you can also rotate the box to see them fall. That's it. No more, no less.